Suture anchors are often used to attach a length of suture to bone in order to use the suture to secure detached soft tissue to the bone. Suture anchors typically have an anchor body, a suture attachment feature, and a bone engaging feature for retaining the suture anchor within bone. The anchor can be inserted into a preformed hole in the bone, and/or the anchor can be self-tapping and thus can include threads for mating the anchor within bone. Most suture anchors require the use of an insertion tool for driving the suture anchor into bone. Such insertion tools are typically formed from an elongate shank having a mating feature formed on a distal end thereof for mating with a corresponding mating feature formed on or in the head of a suture anchor. One common type of driver tool includes a hex-shaped or square-shaped socket for receiving a corresponding hex-shaped or square-shaped head of a suture anchor.
While conventional suture anchors and suture anchor drivers are sufficient, they have some drawbacks. Hex-shaped and square-shaped anchor heads, for example, tend to have a relatively low stripping strength. This can be due to the structural integrity of the anchor head, which is sometimes weakened by the attachment feature used to attach a suture to the anchor head. If the attachment feature decreases the amount of material on the anchor head that interfaces with the driver, then the amount of material that needs to be removed or “stripped” from the drive head is reduced, thus reducing the stripping strength of the head.
Conventional suture anchor heads also tend to have a relatively low failure torque, which can result in shearing of the head during insertion. This type of failure can also be caused by the location of the suture attachment feature on the anchor head, which can reduce the overall cross-sectional area of the drive head. The Bio-corkscrew™ anchor, manufactured by Arthrex Inc., of Naples, Fla., is one example of a suture anchor having a suture attachment feature that can interfere with the structural integrity of the anchor. In particular, a loop is molded into and embedded within the anchor such that the loop extends outward from the head of the anchor to receive a suture. As a result of the placement of the looped suture through the anchor, the entire anchor head is relatively weak and thus has the potential to shear off during insertion.
One option to increase the failure torque of an anchor head is to increase the size of the head. Large anchor heads, however, require a large driver tool, which in turn requires a relatively large bone tunnel to be formed in the bone. This is particularly undesirable, especially where the bone tunnel is to be formed in the cancellous bone. Accordingly, most suture anchors are adapted to for use with a relatively small driver tool, and thus they have a relatively small drive head which can result in a low failure torque and a low stripping strength.
Accordingly, there remains a need for suture anchors having improved physical properties, and in particular having a high failure torque and a high stripping strength.